Today, CyanogenMod began rolling out Release Candidate 1 for their Android 4.2.2-based custom ROM, CyanogenMod 10.1. Currently CyanogenMod 10.1 is available for about 40 different devices and growing. Those forty devices should see their RC1 builds popping up on the CyanogenMod servers very soon if they aren't already there.
If you're already running CyanogenMod, you can go ahead to the built in Update manager and download and install the release candidate without having to flash anything yourself or wipe anything. If you're coming from Stock Android, or another custom ROM, it's a good idea to backup, then wipe data and dalvik cache to be sure nothing weird goes on while you're using CM 10.1.0 RC1. You'll also want to flash Gapps or Google Apps, or you'll find yourself without the Play Store, Gmail, and the rest of Google's apps.
CyanogenMod is a custom firmware developed by a large group of individuals that do this as a hobby. They've added in many features. So it's like stock Android 4.2.2 on steroids. Some of those features include HDR mode for the camera, PIE controls from Paranoid Android, and much more. CyanogenMod has what they call "nightlies" which is a new build releasing every night (or almost every night) or day depending on your time zone. These are somewhat stable, but sometimes things get broken then fixed the next night. So you'll want to be careful with those.
You can find all the builds for each device over on CyanogenMod's website which is linked below. If you want something a bit more "bleeding edge" CyanogenMod has just released their "M snapshot" a few days ago, which are still fairly stable and updated once a month.
So Happy Flashing! Let us know how CyanogenMod 10.1.0 RC1 is going for you in the comments down below.